Ion induced impact ionization detector and uses thereof

ABSTRACT

Disclosed are systems, devices and methodologies relating to an ion induced impact ionization detector and uses thereof. In certain implementations, the detector can include a dielectric layer having one or more wells. An anode layer defining apertures to accommodate the openings of the wells can be disposed on one side of the dielectric layer, and a cathode such as a solid resistive cathode can be disposed on the other side so as to provide an electric field in each of the wells. Various design parameters such as well dimensions and operating parameters such as pressure and high voltage are disclosed. In certain implementations, such an ion detector can be coupled to a low pressure gas volume to detect ionization products such as positive ions. Such a system can be configured to provide single ion counting capability. Various example applications where the ion detector can be implemented are also disclosed.

PRIORITY CLAIM

This application claims the benefit of priority under 35 U.S.C. §119(e)of U.S. Provisional Patent Application No. 61/247,916, entitled “IONINDUCED IMPACT IONIZATION DETECTOR AND HIGH-RESOLUTION IONIZING TRACKSTRUCTURE IMAGING METHOD,” filed Oct. 1, 2009, and U.S. ProvisionalPatent Application No. 61/255,053, entitled “ION INDUCED IMPACTIONIZATION DETECTOR AND USES THEREOF, filed Oct. 26, 2009, each of whichis hereby incorporated herein by reference in its entirety to beconsidered part of this specification.

BACKGROUND

1. Field

The present disclosure generally relates to the field of ion detectors,and more particularly, to systems and methods for detecting ions so asto allow characterization of interaction of ionizing radiation in matterand for utilization in ion-detection based analytic systems.

2. Description of the Related Art

Some detection apparatus and methods rely on electron detection bydetecting current. Although it can be easier to produce and measureelectrons, these methods may not be sufficiently sensitive for certainapplications.

In certain applications, it may be more desirable to analyze orcharacterize a sample or an interaction by detecting positive ions. Suchpositive ions can be generated in a number of ways.

SUMMARY

In certain implementations, the present disclosure relates to an ioninduced impact ionization detector that includes an anode having a firstside and a second side, and defining a plurality of apertures. Thedetector further includes a dielectric layer having a first side andsecond side, where the first side of the dielectric layer is positionedadjacent the first side of anode, and the dielectric layer has athickness of approximately 1-50 mm. The detector further includes aplurality of wells extending through the dielectric layer, with theplurality of apertures of the anode positioned relative to the pluralityof wells so as to define openings between the plurality of wells and thesecond side of the anode. The detector further includes a cathodepositioned adjacent the second side of the dielectric layer forming abottom of each of the plurality of wells.

In certain embodiments, the thickness is in a range of approximately 1to 5 mm. In certain embodiments, the thickness is in a range ofapproximately 2 to 5 mm.

In certain embodiments, the anode includes one or more layers ofconductive material. In certain embodiments, the cathode includes aresistive cathode layer.

In certain embodiments, the anode and the cathode are separated by adistance that is substantially the same as the thickness of thedielectric layer.

In certain embodiments, the ion induced impact ionization detector issensitive to a single ionization event in each of the plurality ofwells.

In certain embodiments, the ion induced impact ionization detectorfurther includes a first plurality of readout strips configured in afirst orientation and disposed on the first side of the dielectriclayer. The detector further includes a second plurality of readoutstrips configured in a second orientation and disposed on the firstplurality of readout strips so as to allow identification of a well thathas detected an ion. In certain embodiments, the first and secondorientations are substantially perpendicular so as to define X and Yorientations.

In certain embodiments, the ion induced impact ionization detectorfurther includes a third plurality of readout strips configured in athird orientation and disposed on the second plurality of readout stripsso as to allow determination of more than one wells that detected ionssubstantially simultaneously. In certain embodiments, the first, secondand third orientations define X, U and V orientations.

In certain embodiments, each of the plurality of wells has a cylindricalshape, and each of the openings defines a circle having a diameter. Incertain embodiments, the diameter is selected to be in a range of aboutone-tenth of the thickness to one thickness. In certain embodiments, thediameter is selected to be in a range of about one-fourth of thethickness to one-third of the thickness.

In certain embodiments, the plurality of wells are arranged in an arrayso as to define a pitch distance between the edges of two neighboringopenings, with the pitch selected so that a ratio between the pitch andthe diameter is in a range of about 1 to 5. In certain embodiments, theratio between the pitch and the diameter is in a range of about 1.1 to3.

In certain implementations, the present disclosure relates to a detectorsystem that includes an enclosure having a volume of low pressure gas.The system further includes a drift anode disposed within the volume oflow pressure gas. The system further includes the ion induced impactionization detector as summarized above disposed within the volume oflow pressure gas so as to define a detection gas volume between thedrift anode and the anode of the ion induced impact ionization detector,with the wells having substantially the same low pressure as in thevolume of low pressure gas due to the openings. The system furtherincludes an electrical power supply coupled to the drift anode, and theanode and cathode of the ion induced impact ionization detector. Theanode of the ion induced impact ionization detector is at a groundpotential, the drift anode is at a positive potential relative to theground, and the cathode is at a negative potential relative to theground. The positive potential selected to provide a first electricfield in the detection gas volume for drifting of a positive ion towardsthe anode of the ion induced impact ionization detector. The negativepotential selected to provide a limited Geiger avalanche in the wellwhere the positive ion drifts into.

In certain embodiments, the low pressure of the gas is in a range ofabout 1 to 100 Torr. In certain embodiments, the low pressure of the gasis in a range of about 1 to 10 Torr.

In certain embodiments, the negative potential is selected such that anelectric field strength within the well is greater than a thresholdvalue associated with breakdown of the gas in the well. In certainembodiments, the negative potential is selected such that the electricfield strength within the well is less than a threshold value associatedwith field emission breakdown at a surface of the well.

In certain embodiments, the negative potential is selected such that anelectric field strength within the well puts the gas within the well ina super-tensioned state.

In certain embodiments, one or more dimensions of the well, spacingbetween the wells, and the negative potential is selected such that anelectric field formed within the well is capable of changing as the ioninduced avalanche progresses to direct another incoming ion to anothernearby well.

In certain implementations, the present disclosure relates to a methodof detecting particles. The method includes detecting one or morepositive ions using the ion induced impact ionization detectorsummarized above.

In certain embodiments, the method further includes subjecting thesecond side of the anode to a gas, and maintaining the environmentsurrounding the ion induced impact ionization detector at a pressure ofless than about 10 Torr.

In certain embodiments, the method further includes applying a negativevoltage to the cathode, and maintaining the anode at ground potentialsuch that an avalanche breakdown of the gas in the wells results when apositive ion enters the sell, with the avalanche resulting in adetectable collection of charges.

In certain embodiments, the negative voltage applied is in a range ofabout 600-900V, and the operating pressure is selected to be less thanabout 10 Torr. In certain embodiments, the operating pressure isselected to be less than about 2 Torr, and the negative voltage isselected so as to yield a quantity of electric field strength divided bypressure (E/p) has a value of about 2000V/(cm Torr).

In certain implementations, the present disclosure relates to a methodfor modeling a sample of condensed matter. The method includesidentifying ionization clusters responsible for local damage to thecondensed matter.

In certain embodiments, the condensed matter is selected from the groupconsisting of cells, polymers, nanoelectronics and nucleic acidmolecules.

In certain embodiments, the method further includes subjecting thecondensed matter to ionizing radiation produced by the ion inducedimpact ionization detector summarized above, where the subjecting stepinduces an aberration in the condensed matter. In certain embodiments,the method further includes assessing effects of the ionizing radiationon the condensed matter. In certain embodiments, the effects areselected from a DNA double strand break, a central nervous systemeffect, and cancer induction.

In certain implementations, the present disclosure relates to a methodof track ion detection. The method includes imaging a spatialdistribution of initial energy deposits in condensed matter by detectingpositive ions using the ion induced impact ionization detectorsummarized above.

In certain embodiments, the method further includes correlatingmeasurements from the imaging step with radiation effects in thecondensed matter. In certain embodiments, the ion induced impactionization detector provides a substantially full topology of theionization pattern of track segments and resolves single and clusteredionization events along the radiation track over a length in condensedmatter.

In certain implementations, the present disclosure relates to a trackion detector having the ion induced impact ionization detectorsummarized above.

In certain implementations, the present disclosure relates to a massspectrometer, an ion mobility spectrometer or a gas chromatographincluding the ion induced impact ionization detector summarized above.

In certain implementations, the present disclosure relates to a particledetector for detecting the presence and location of a particle. Thedetector includes a first electrical plate, and a second electricalplate. The first and second electrical plates are biased with respect toeach other so as to define an electric field therebetween. The detectorfurther includes an insulating layer interposed between the firstelectrical plate and the second electrical plate so as to be positionedwithin the electric field. The insulating layer includes a plurality ofwells that extend therethrough, where the wells are spatiallydistributed so as to receive particles. The wells include openingthrough which particles can enter. The detector further includes atleast one sensor that is positioned with respect to the wells so as toprovide signals indicative of the presence of particles within thewells. The electric field, the length of the wells and the atmospherewithin the wells are selected so that a charged particle entering thewells results in a limited Geiger avalanche breakdown within the wellsthereby resulting in a detectable signal by the sensor indicative of theparticle entering the wells.

In certain embodiments, the ratio of the pitch to the well diameter isabout 1.1 to 3. In certain embodiments, the wells have a length ofapproximately 2-5 mm and the atmosphere within the wells is maintainedat a pressure of approximately less than 10 Torr, the diameter of thewells is about 0.1-2 mm, and the pitch is about 0.2-5 mm. In certainembodiments, the pressure is less than about 2 Torr, the wells have alength of about 3.2 mm, the diameter of the wells is about 0.8 mm, andthe pitch is about 2 mm. In certain embodiments, the detector includesabout 1-10,000 wells.

In certain embodiments, the particle detector further includes at leasttwo readout strip layers configured to determine the relative locationof detected ions.

In certain implementations, the present disclosure relates to a methodfor detecting the presence and location of a positive ion. The methodincludes establishing an electric field in a low pressure gaseousenvironment to generate ions, where the electric field is sufficient tocreate a limited Geiger avalanche breakdown. The method further includesdetecting a signal produced by the avalanche breakdown.

In certain implementations, the present disclosure relates to aradiation dosimeter that includes a first electrode layer. The dosimeterfurther includes a second electrode layer having first and second sides,where the first side of the second electrode layer and the firstelectrode layer define an interaction region occupied by gas moleculesat a pressure, and where the second electrode layer defines a pluralityof apertures to allow passage of charged particles generated fromionization of the gas molecules by radiation passing through theinteraction region. The dosimeter further includes a third electrodelayer disposed on the second side of the second electrode layer. Thedosimeter further includes an insulating layer interposed between thesecond electrode layer and the third electrode layer, where theinsulating layer defines a plurality of wells open towards theinteraction region. The wells are spatially distributed so as tosubstantially match the plurality of apertures of the second electrodelayer and so as to receive the charged particles passing therethrough.The dosimeter further includes a voltage control circuitry configured toprovide the first, second, and third electrode layers with differentelectrical potentials, such that the interaction region is provided witha first electric field that allows drifting of the charged particlestowards the second electrode layer without charge multiplication. Thewells are provided with a second electric field that results in chargemultiplications in wells where the charged particles enter. Thedosimeter further includes a detection circuitry in communication withat least one of the second and third electrode layers and configured todetect the charge multiplications in the wells.

In certain embodiments, the charged particles include positive ionsgenerated from the ionization. In certain embodiments, the secondelectrode layer is electrically connected to an electrical ground. Incertain embodiments, the first electrode layer is provided with apositive potential relative to the electrical ground so as to allowdrifting of the positive ions towards the second electrode layer. Incertain embodiments, the third electrode layer is provided with anegative potential relative to the electrical ground so as to allowacceleration of the positive ions in the wells to induce the chargemultiplications.

In certain embodiments, the interaction region is dimensioned and thepressure is selected such that an ionization cross-section in theinteraction region is similar to an ionization cross-section of anano-scale condensed matter object. In certain embodiments, the pressureis selected to be less than approximately 10 Torr so as to allowrelatively large expansion of the interaction region dimension toapproximate the ionization cross-section of the nano-scale condensedmatter object. In certain embodiments, the wells' depth is selectedbased on the selected pressure and its corresponding range of electricfield strength per pressure (E/p) values where the charge multiplicationoccurs. In certain embodiments, the wells' depth is selected based onprobability of the charge multiplication yielding sufficient detectablecharge. In certain embodiments, the wells' depth is selected to reducelikelihood of dielectric breakdown of the insulating layer. In certainembodiments, the wells' depth is selected to be about 2 mm or greater.In certain embodiments, the wells' depth is selected to be between about2 mm and 5 mm.

In certain implementations, the present disclosure relates to aradiation dosimetry method that includes providing a gaseous volume suchthat radiation passing through the volume has a probability ofionization interaction with gas molecules at a pressure that is similarto a probability of ionization interaction of the radiation with anano-scale condensed matter object. The method further includesproviding a first electric field to the gaseous volume so as to inducedrifting of one or more positive ions generated from one or more ionizedgas molecules to a first side of the gaseous volume. The first electricfield is selected for the gas molecules at the pressure so as to resultin the drifting but not in charge multiplication from the one or morepositive ions or corresponding electrons. The method further includesdetecting the one or more drifting positive ions at the first side so asto characterize the ionization interaction in the gaseous volume. Thepressure of the gas molecules and dimension of the gaseous volumetraveled by the radiation are selected such that the characterization ofthe ionization interaction in the gaseous volume approximates theionization interaction of the radiation with the nano-scale condensedmatter object.

In certain implementations, the present disclosure relates to an iondetector element that includes an anode and an insulator layer having afirst side and a second side. The first side of the insulator layer isdisposed adjacent the anode, and the insulator layer has a thickness ina range of approximately 1-5 mm. The ion detector element furtherincludes a cathode disposed adjacent the second side of the insulatorlayer. The insulator layer defines a well that extends between the firstand second sides of the insulator layer. The well is provided with a gasat a pressure of approximately 1-10 Torr. The anode and cathode providedwith an electrical potential difference of approximately 600-900 V.

In certain implementations, the present disclosure relates to a gaschromatograph having one or more of the ion detector elements summarizedabove.

In certain implementations, the present disclosure relates to an ionmobility spectrometer including one or more of the ion detector elementssummarized above.

In certain embodiments, the spectrometer is configured to detect traceamounts of one or more chemicals associated with explosives, drugs, andchemical weapons.

In certain implementations, the present disclosure relates to an iondetector having a plurality of the detector elements summarized abovearranged in an array so as to allow spatial determination of ionsincident of the detector elements. In certain implementations such anarray can be part of a dosimeter. In certain implementations such anarray can be part of a mass spectrometer.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features of the inventions have been described herein. It isto be understood that not necessarily all such advantages may beachieved in accordance with any particular embodiment of the invention.Thus, the invention may be embodied or carried out in a manner thatachieves or optimizes one advantage or group of advantages as taughtherein without necessarily achieving other advantages as may be taughtor suggested herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts an example of an ion-counting system whereionization-induced ions are generated in a low-pressure gas volume andextracted into an ion-counter in a high-vacuum environment.

FIG. 2A show distributions of sizes of ion-clusters that can be inducedby protons, alpha-particles and carbon ions, in a gas volume of propaneat about 1 Torr.

FIG. 2B shows a comparison of Monte-Carlo model simulations with theexperimental data over 3.5 orders of magnitude.

FIG. 3 shows that in certain implementations, a two-dimensional array ofion detectors can be configured to detect ions such as those resultingfrom ionization in a gas volume, where the ion detector array can beoperated in a similar gas pressure environments as that of the gasvolume.

FIG. 4A depicts a portion of a two-dimensional ion detector that can beused for a number of purposes including imaging, where the detector caninclude an array of wells formed in a dielectric layer.

FIG. 4B shows a more detailed view of one of the wells of the detectorin FIG. 4A.

FIG. 5 shows examples of calculated energy distributions of radiationinduced ions that are drifting in propane across a well under a field ofapproximately 1000V per 0.1 mm.

FIGS. 6A and 6B show example electric field lines in a well during andclose to termination of a limited-Geiger avalanche triggered by apositive ion.

FIG. 7 shows a portion of a detector apparatus having a number of wellsconfigured to facilitate ion induced impact ionization.

FIG. 8 shows that in certain embodiments, the detector apparatus of FIG.7 can be fabricated on a printed circuit board (PCB).

FIGS. 9A and 9B show examples or readout electrode strips that can beimplemented in the detector apparatus of FIG. 8.

FIG. 10A shows an experimental setup using alpha-particles for testingthe detector of FIG. 8.

FIG. 10B shows examples of signals that can be extracted from theexample setup of FIG. 10A.

FIG. 11A shows an example distribution of charge resulting from thedetector of FIG. 8 operating at approximately 800 V in propane atapproximately 3 Torr pressure.

FIG. 11B shows that in certain implementations, the mean signalamplitude corresponding to the charge output of FIG. 11A can depend onthe operating voltage.

FIG. 12 shows example plots of lateral resolution (rms) intissue-equivalent (TE) units for ions following a drift path ofapproximately 40 nm in approximately 1 Torr propane.

FIG. 13 schematically depicts an example application where interactionsof radiation in a volume of low pressure gas can provide an estimate ofan equivalent dose of the radiation delivered to a nano-scale condensedmatter.

FIG. 14 shows an example process that can be implemented to facilitatethe dosimetry system of FIG. 13.

FIG. 15 shows that in certain implementations a gas model can simulate acondensed matter such as a DNA molecule, thereby allowingcharacterization of its interaction with radiation at a large expandedscale.

FIG. 16 shows an example configuration of an interaction volume of gaswhere ionization products can be generated, collected and detected.

FIG. 17 shows an example process that can be implemented to facilitatedetection of single ions resulting from events such as the ionizationoccurring in the gas interaction volume of FIG. 17.

FIG. 18 shows an example configuration of a well based detector that canachieve detection of single ions.

FIG. 19 schematically depicts an example of how data can be acquiredfrom detection of ions in an analytic system.

FIG. 20 schematically depicts various components that can be provided toa system capable of facilitating the process of FIG. 19.

FIG. 21 schematically depicts an ion detector element capable ofdetecting single ions.

FIG. 22 schematically depicts an array having a number of the detectorelements of FIG. 21.

FIG. 23 schematically depicts an analytic system having the detectorarray of FIG. 22.

FIGS. 24A-24C show non-limiting examples of systems having one or moreof the detector element of FIG. 21.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The headings provided herein, if any, are for convenience only and donot necessarily affect the scope or meaning of the claimed invention.

In embodiments described herein, a gas-based detector can addressvarious issues associated with detector designs. As also describedherein, scaled dimension (e.g., nanometer scale) equivalent resolutionis achievable using one or more features of the present disclosure. Sucha resolution capability can be implemented in a number of applicationsand provide various benefits. For example, patients can benefit becausetreatment planning of proton and heavy ion radiation therapy can be mademore precise by taking the varying biological effectiveness of theseparticles into account. In another example, society at large can benefitby allowing better definition of radiation exposure limits and therebyprotecting its members from unwanted side effects of radiation such ascancer and genetic alterations.

In yet another example, high-resolution imaging of radiation trackstructure can be achieved using one or more features of the presentdisclosure. Such a capability can be relevant in many technical fieldsrelated to radiation interaction with matter, such as in medicine,physics, radiobiology, and engineering.

Examples for applications or potential applications of track structureimaging in medicine can include optimization of treatment planning fortherapy with particles such as protons and heavy ions, and evaluation ofspace radiation for cancer risk estimates. Applications in other fieldscan include solar neutrino studies, dark matter search, x-raypolarimetry in astrophysics, radiation protection, nuclear wastemanagement, radiation therapy planning with charged particles, mannedspace missions and damage to micro- and nano-electronic elements inintense radiation fields in accelerator and outer space environments. Incertain implementations of the present disclosure, nanometer-equivalentresolution capability can be applied to some or all of the foregoingexample applications.

An important field that can benefit from precise track-imaging devicesis the study of radiation damage to cells and DNA. Current devices andmethodologies for track-imaging, however, are generally not suitable fortrack-structure studies on the DNA-to-chromosome scales. In certainsituations, study of interactions at such nanometer-scales can befacilitated by detectors and devices that are sometimes referred to asnanodosimeters.

In certain implementations of the present disclosure, a device (e.g., ananodosimeter) can be configured to detect positive ions which areinduced by particle radiation in a low-pressure gas (e.g., propane ofabout 1 Torr). The use of the low gas pressure allows scaling down amillimeter-size gas volume from which ions are collected to anequivalent unit density volume of nanometer size. In this particularexample, the scaling is by a factor of about 10⁻⁶. The nanodosimeterthus can simulate a short segment of DNA of about 20 nm in length and2-4 nm in diameter.

In certain implementations, the foregoing example nanodosimeter can beconfigured to a frequency of ion clusters of different sizes formed insuch a volume. Such information can be of interest for biomedicalapplications due to, for example, a hypothesis that large clusters,despite being relatively rare, are mainly responsible for irreparableDNA damage in a living cell.

There are a number of ways for detecting ionization products such aspositive ions. For example, FIG. 1 schematically depicts an embodimentof an ion-counting nanodosimeter 10. Ionization-induced ions are shownto be deposited in a sensitive volume such as a volume of low-pressuregas (e.g., 1 Torr propane). The ions formed in such a volume,representing, for example, a DNA segment, are shown to be extracted intoa high-vacuum ion-counter, where they are multiplied and individuallydetected and counted. The number of ions formed in the sensitive volumecan be proportional to the deposited energy; and the detectable timedelays along a pulse trail can provide information about the interactionlocation along the sensitive volume (DNA) axis.

In certain embodiments, information obtained from such ion measurementscan be used to characterize different types of radiation at variousenergies. Such characterization of radiation and its representativeinteraction with matter (e.g., nano-scale condensed matter) can be used,for example, to refine simulation models.

For example, FIG. 2A shows various ion-cluster size distributionsinduced by protons, alpha particles and carbon ions, in the examplesensitive volume of the nanodosimeter described in reference to FIG. 1(operated at approximately 1 Torr of propane gas). FIG. 2B shows acomparison of Monte-Carlo model simulations, where there is substantialagreement with experimental data over 3.5 orders of magnitude, as wellas divergence in other regions. Such differences can be addressed in themodel appropriately.

In the example of FIGS. 1 and 2, counting of ions is performed at aselected location with respect to the sensitive volume; and spatialinformation about the ionization events are obtained from the ion pulsetrain.

In accordance with certain implementations of the present disclosure, anion induced impact ionization detector described herein can permitsubstantially full track structure imaging. In certain embodiments, theion induced impact ionization detector described herein can have asensitive volume with a simple geometrical shape (e.g., a cylinder, asphere or a box). In certain implementations, the ion induced impactionization detector described herein may be used to measure acorrelation of clustered ionization events over chromosomal-equivalentdimensions.

In certain embodiments, there is no significant pressure differencebetween the sensitive volume and the ion counter; thus obviating adouble differential pumping system (e.g., a system having twoturbomolecular pumps) generally associated with the example device ofFIG. 1. Therefore, the ion induced impact ionization detector describedherein can be relatively compact, mobile and inexpensive. The lack of asignificant pressure gradient can also minimize the distortion ofionization clusters as the clusters move through the gradient.

In certain implementations, one or more features of the presentdisclosure can be related to nanodosimetry track-structure imagingmethods that can provide a substantially full topology of the ionizationpattern of track segments and efficiently resolve single and clusteredionization events along the radiation track over a length in condensedmatter.

In certain implementations, a low-pressure (e.g., ˜1 Torr) gaseousdetector can be provided. FIG. 3 schematically depicts a gaseousdetector 100 having a volume (D1×D2×2D3 in lab frame, andD1TE×D2TE×2D3TE in tissue-equivalent representation) of gas (102) whereionizations are shown to be induced along a given track segment of anionizing particle. For example, each of D1TE and D2TE can have a TEdimension of about 100 nm. Examples of D3TE dimensions are discussedbelow.

Primary ionizations are indicated as 120; secondaries as 122. Clusterformations are indicated as 124. The ionization products are depicted asdrifting (arrows 130) towards a detection plane 110. In certainembodiments, the detection plane 110 can include a two-dimensional arrayof positive-ion detectors as described herein.

The detection plane 110 shown in FIG. 3 can be positioned on one side ofthe gas volume 102. In certain embodiments, the gas volume 102 and/orthe positioning of the detection plane 110 can be selected so as to keepthe drift distances of the induced ions to the detection plane as 110small as possible. For example, according to a calculated estimate, atissue-equivalent (TE) cylinder (depicted by circles 104 at the entranceand exit of the gas volume) of about 16 to 40 nm radius (D3TE in TErepresentation) centered about the primary track contains about 95% ofthe ionizations (primaries 120 and secondaries 122) induced by 1 to 100MeV protons, respectively. In propane of 1 Torr, this corresponds toradius range of about 6 to 15 mm (D3 in the lab frame).

Interaction of radiation with the detector gas can lead to a trail ofmolecular excitations and ionizations. The latter, in the form ofelectron-ion pairs, can be utilized in micro- and nanodosimetry for themeasurement of the deposited energy as well.

In certain implementations, various detector parameters such as thedetector size, including the drift length in the laboratory frame,l_(LAB), and the cell size can be based on the gas pressure. Generally,the higher the pressure, the cell size and the overall detectordimension can be smaller. For example, at 1 Torr of propane (with ascale conversion of 1 mm gas being equivalent to about 2.6 nm TE), thevertical size (representative of an upper limit in drift length) of thedetector can be about 6 and 15 mm for 1 and 100 MeV protons,respectively. In some embodiments, in order to image tracks of about 1μm length, the imaging plane of the detector can have a size ofapproximately 400×400 mm². The cell size in such a detector can be about0.2 mm² (approximately 0.5 nm² TE cells).

FIG. 4A shows a portion 160 of an array of detection cells 154. FIG. 4Bshows an expanded view of one of the detection cells of FIG. 4A.

In the example shown, a relatively large number of independentwell-based gaseous detectors 164 can be provided. In certainembodiments, the detectors 164 can operate in a limited Geiger mode(fired/not fired).

The use of a relatively large number of individual detecting cells canprovide high detection efficiency for single ions, despite therelatively large dead time that may exist in individual cells operatingin Geiger mode. Due to the diffusion of the ions, at low gas pressures,even ions originating from the same deposition point will likely beregistered in different cells. Hence, the effective counting efficiencyof some embodiments can be very high.

In certain implementations, each gaseous detector 164 can be configuredto multiply an ion 176 incident therein. Individual positive ions,originating from radiation-induced primary and secondary(delta-electrons) ionizations along the track of a charged particle, maydrift under an electric field across-the interaction volume to theion-multiplier 164. In some embodiments, the ion-multiplier 164 can havea hole-type detector structure such as the ones shown in FIGS. 4A and4B.

In certain embodiments, the ion-multiplier 164 can be configured to havesome similarities with devices such as what is sometimes referred to asa micro-well detector (MWD). Unlike the MWD device, however, certainembodiments of the ion-multiplier 164 can operate in a limited Geigermode under reversed polarity.

More particularly, a typical MWD device is designed to be triggered byan electron entering the micro-well. Accordingly, an anode is typicallyplaced at the bottom of the micro-well, and a cathode at the entrancesurface. Thus, electrons resulting from the multiplication process inthe micro-well are thus accelerated to the anode, and charge signals canbe collected therefrom.

As described herein, certain embodiments of the present disclosure caninclude an arrangement of electrodes that are substantially reversedfrom typical MWD devices. In such a reverse-polarity arrangement, acathode can be positioned at or near the bottom of a well, and an anode(relative to the cathode) at or near the entrance surface. Variousnon-limiting examples of such a configuration—by itself or incombination with a detection gas volume—are described herein in greaterdetail.

It is noted that some embodiments of an MWD device can include a denselyperforated holes formed on relatively thin insulator layer (e.g., anapproximately 50 μm-thick Kapton layer with a thin metal clad on each ofboth faces. Such an insulator layer can include holes (e.g., 50 μmdiameter). In such a configuration, and with the foregoing MWD polarityof electrodes, radiation-induced electrons can be focused into the wellsand be multiplied therein.

In certain embodiments, the detector array 160 can be much thicker thanthe foregoing MWD example. The insulator layer (162) can have athickness in a range of about 1-5 mm, and its upper surface can beprovided with thin metal strips as readout strips 166. Each of the holescan have a diameter in a range of about 0.5-1 mm; and the holes can bespaced by a distance in a range of about 200-1000 μm. In someembodiments, to obtain a Geiger mode of operation, a highly resistiveelectrode layer (168) can replace the conductive layer at the bottom ofthe well.

In certain embodiments, the focusing of an ion into the well 164 and thecharge multiplication process within the well can be controlled by anelectric field across the well. Such an electric field can be providedby applying a negative voltage to the lower resistive electrode 168. Theupper electrode 166 can be formed of strips common to each row of holes,and be kept at a ground potential.

It is noted that a well-based detector having a relatively smallseparation distance between the electrodes can be provided with anoperating voltage difference between the electrodes. Approximating thearrangement of such electrodes as parallel plates, such a voltagedifference (V) can be represented by the electric field strength (E)times the separation distance (d). To maintain the same electric fieldstrength within the well (so as to provide a similar detection process)for a relative thicker dielectric configuration, the correspondingincrease in separation distance (d) makes it necessary to increase thevoltage (in a linear manner). Utilizing such a relatively thickdetectors in certain operating conditions can result in a large andpotentially harmful voltage difference.

An ion entering the cell 164 can undergo collisions with gas moleculesand/or positive-ion impact ionizations of the gas to yield an electronavalanche 180. In addition, the ion can collide with the walls or bottomelectrode of the cell, resulting in secondary electron emission (182 inFIG. 4B). Cross sections for such ionizing ion-gas collisions can dependon the type of gas, gas pressure and on the electric field strengthassociated with the cell. Available data for positive ion impactionizations are relatively scarce; thus, available data for 0₂-N₂collisions (J. B. Hasted, Physics of Atomic Collisions, LondonButterworths, 1964) were used to obtain some rough estimations herein.

For example, referring to FIG. 5, energy distributions of ions in a 0.1mm thick well were obtained with an ion transport model configured forcalculations for embodiments of the ion counting nanodosimeter describedherein.

The resulting estimated probabilities for gas ionization by positiveions are presented in Table 1. The values listed in Table 1 areapproximate values. The listed probability for each gas pressure is aprobability for at least one gas ionization in a well of approximately0.1 mm depth under an electric field strength of approximately1,000V/0.1 mm.

TABLE 1 Pressure, Mean energy Probability of at Torr of ions, eV leastone ionization 1 470  15% 10 50 2.5% 100 5 0.25% 

The values presented in Table 1 assume that ionizations are only causedby ion-molecule collisions. Charge-exchange collisions, resulting infast neutral molecules, can also induce ionizations but with far lowerprobabilities. These rough estimations show that collision ionizationsin the gas phase have a very low probability to create secondaryelectrons (at best 0.15 at 1 Torr), and will, therefore, not provide adesired efficiency for detecting ions. Therefore, micro-pattern detectorthickness of about 0.1 mm is generally too small for providing highefficiency of single positive ion registration. Accordingly, a thicker(e.g., a few mm) detector structures can be provided to yield highprobability (e.g., close to 100% probability) of ion impact ionizationas the ion travels in the cell.

The ionization probability can also be increased by providing higherelectric field strength. However, such a higher electric field canresult in field emission breakdown that can permanently damage thedetector structure.

In the limited Geiger mode, the electrons can initiate a substantiallyunrestricted avalanche in the cell hole; and such an avalanche candevelop due to ionizing collisions of secondary electrons with the gasmolecules. The process, once started, can go on until substantially allgas in the hole is ionized. A discharge can develop, unless the electricfield is restricted by space charge effects and/or by an external deviceor circuit (e.g., a resistor in the high-voltage bias chain), as in aGeiger counter. In certain situations, the discharge can be stopped whenthe voltage drops due to the high volume resistivity of the cell'sbottom negative electrode.

In the limited Geiger mode, each cell can operate as an independentGeiger micro counter, and an output signal can determined by the chargeaccumulated in the cell's capacitor. Such a charge can be represented asQ_(CELL)=C_(CELL)V, where C_(CELL) is the capacitance and V is theoperating voltage across the cell. Depending on the cell size, C_(CELL)can of the order of tens of fF (femtofarad); thus for V in a range ofabout 500 to 1000V, Q_(CELL) value in the tens of pC (picocoulomb) rangecan be expected. In certain implementations, such a charge output can beread out and processed.

Recovery time of the cell can depend on the charge collection time andrecharging time; and the former is expected to be in a sub-μs to μsrange. In embodiments where the gas pressure is low (e.g., about 1Torr), such a recovery time generally should not affect the iondetection efficiency; and in particular, at relatively low ionizationdensities. In such ionization densities, more than one ion entering thesame cell is quite rare. Further, ions will likely arrive spaced in timedue to their relatively low drift velocities (e.g. about 0.05 cm/μs in 1Torr propane, at 100 V/(cm Torr)).

A detector operating as a micro-Geiger cell structure 232 can include afeature where the electric field 230 configuration can change during thedischarge development within a hole. It can be a dynamic process thatcan be explained on the basis of the electron trajectories shown inFIGS. 6A and 6B before, during, and close to the end of the dischargeassociated with electrons 234. As one can see, majority of secondaryelectrons 234 are collected on the strips in an initial stage of thedischarge (FIG. 6A), because they are produced in the vicinity to thestrips.

The cell field can drop due to the positive charge of the ions screeningthe charge on the resistive electrode at the bottom of the well. Thefield of non-active neighboring cells can expand to the vacant region totrap remaining electrons which otherwise would drift upwards to theionization volume and deflecting any subsequently arriving ion into anearby vacant cell. The remaining electrons can be slowly collected inthe reduced field configuration, again by the strips (FIG. 6B).

In certain situations, some electrons can escape the trap or hit thecell's sidewalls. Such a dynamic process and estimating effects such aselectron escape and possible wall up-charging can be difficult tosimulate.

A detected signal can be induced by electrons extracted from the celland collected by grounded electrode strips. In the Geiger mode, suchreadout strips can be deposited on the cell's anode. Additional pick-upstrips (e.g., 170 in FIG. 4A) on the lower side of the negativeelectrode can provide a second coordinate. Alternatively, a pixelized 2Dreadout circuit can be directly coupled to the bottom of the device andmeasure avalanche-induced signals. With such a readout system, thedetector can provide a 3D image of the track, where a strip or padreadout circuit can provide the 2D position of the detected ion, and thepulse timing signal can provide the third coordinate.

In certain embodiments, an optical readout technique can be implemented.Such a configuration can include recording avalanche-induced photonswith a sensor such as an intensified CCD camera system. The CCD cameracan provide a 2D image of the track, and the third coordinate can beprovided by simultaneously recording the avalanche-light flashes withphotomultiplier tubes. In the example detector configuration shown inFIG. 4A, an optical readout component 174 can include such a sensor(e.g., CCD camera). Further, an optical element 172 such as a lens canfacilitate delivery of light signals to such an optical readoutcomponent 174.

FIG. 7 depicts an example ion detector 351. It will be understood thatsuch a depiction is not necessarily to scale. The detector 351 caninclude a number of cells formed on a dielectric layer or an insulatinglayer 352. The dielectric layer 352 can include but not limited toinsulator materials such as ceramic, silicon dioxide, oxidized surface,porcelain or the like with negligible electrical conductivity. Incertain embodiments, a printed circuit board insulator (e.g., FR4) canbe used as the insulating layer 352. In certain embodiments, one side ofthe dielectric layer 352 is adjacent an anode layer 354, and the otherside is adjacent a cathode layer 356 (e.g., a glass cathode layer). Incertain embodiments, the dielectric layer 352 can be directly adjacentto the anode 354 and/or cathode layer 356, so that there is nointervening layer.

In some embodiments, a distance between the two electrical plates orelectrodes 354, 356 defining an inter-electrode gap distance can besimilar to or approximately the same as the thickness (353) of thedielectric layer 352. In certain embodiments, such an inter-electrodegap distance can be in a range of about 1 mm to few cm (e.g., 5 cm). Incertain embodiments, the gap distance can be in a range of about 1 mm to5 mm. In certain embodiments, the gap distance can be in a range ofabout 2 mm to 5 mm. In the example detector described in reference toFIGS. 7 and 8, the gap distance can be approximately 3.2 mm. In certainembodiments, the gap distance between the electrodes 354, 356 may or maynot be the same as the thickness of the dielectric layer 352.

In certain implementations, an increase in operating gas pressure can beaccommodated with a decrease in the inter-electrode gap distance. Thus,for example, for a gas pressure of about 10 Torr, a gap distance in arange of about 1-2 mm may be appropriate. For a lower gas pressure ofabout 1 Torr, a gap distance of about 5 mm may be appropriate. In theexample detector described in reference to FIG. 8 where theinter-electrode gap distance is about 3.2 mm (e.g., a thickness of aPCB), a gas pressure of about 2 Torr can be appropriate for ionmeasurements.

In certain implementations, the inter-electrode gap distance and/or thegas pressure can be adjusted for different types of gases.

In certain embodiments, the anode layer 354 may be formed fromconductive materials such as metal (e.g., silver or copper). The anodelayer 354 may be further coated with materials such as inert metal(e.g., gold or palladium). The anode layer 354 may include openings thatsubstantially align with the openings of the wells 355 in the dielectriclayer 352.

In certain embodiments, the anode layer 354 can include strips common toeach row of wells 354. In certain embodiments, the anode layer 354 candefine openings corresponding to well-openings but otherwisesubstantially cover one side of the dielectric layer 352. In certainembodiments, the anode layer 354 can be substantially continuous ordiscontinuous, and can cover at least a portion of the dielectric layer352.

In certain implementations, the cathode layer 356 can include anelectrode on one side of the dielectric layer 352 opposite from the sidewhere the anode layer 354 is positioned. In certain embodiments, thecathode layer 356 can include a resistive cathode that can be formedfrom optically transparent or semitransparent materials such asconductive glass if optical detector readout is desired or implemented.In certain embodiments, the resistive cathode can include resistiveKapton, conductive ceramic, or composite material such as rutheniumresistive paste fired on appropriate substrate (e.g., silica, glass).

In certain embodiments, the resistive cathode 356 can be a layer whichforms the bottom (357) of the well 355 in the dielectric layer 352. Theresistive cathode 356 may or may not be directly adjacent the dielectriclayer 352. In certain embodiments, there is no intervening layer such asmetal between the resistive cathode 356 and the dielectric layer 352.

The dielectric layer 352 can define wells 355 having openings 362 formedon the side adjacent the anode layer 354. The anode layer 354 can alsodefine similarly dimensioned and positioned opening. In certainimplementations, such openings can be formed by techniques such asreactive ion etching, printed circuit board (PCB) technology, or otherappropriate methods. In the example shown in FIG. 8, the wells 355extend to the upper surface of the cathode 356 so that the cathode 356defines a floor 357 of each well 355.

For the purpose of description of FIG. 8, the wells are sometimesreferred to as cells.

In certain embodiments, the openings 362 allow the wells 355 to be incommunication with a gas volume (not shown) above the detector 351.Thus, the wells 355 can be occupied by the same gas at substantially thesame pressure as that of the gas volume.

In the particular example 351 described in reference to FIG. 8, thedielectric layer 352 has a thickness (353) that is about 3.2 mm thick.Each of the wells 355 is cylindrically shaped, and has a diameter (364)of about 0.8 mm. The wells 355 are arranged in an array with a pitch(363) of about 1 mm.

In certain implementations, the dielectric layer thickness 353 can beless than or equal to the gap distance between the electrodes 354, 356.Accordingly, in certain embodiments, the thickness 353 can be in a rangeof about 1 mm to few cm (e.g., 5 cm). In certain embodiments, thethickness 353 can be in a range of about 1 mm to 5 mm. In certainembodiments, the thickness 353 can be in a range of about 2 mm to 5 mm.In the example detector described in reference to FIG. 8, the thickness353 can be approximately 3.2 mm.

In certain implementations, wells described herein can include aplurality of holes 355 in the dielectric layer 352. The holes may have arelatively simple geometric shape such as cylindrical or rectangularshape. In certain embodiments, the well opening 362 or the crosssections of the wells 355 can be substantially round.

In certain implementations, diameter 364 of each hole can be in a rangeof about 0.1-2 mm, 0.5-1.5 mm, 0.6-1 mm. In the example detector of FIG.8, the diameter is about 0.8 mm.

In certain implementations, the diameter 364 of each of each well 355can be selected based on the thickness 353 of the dielectric layer 352.In certain embodiments, a ratio between the diameter and thickness canbe in a range of about 1/10 to 1/1. In certain embodiments, the ratiocan be in a range of about 1/4 to 1/3. In certain embodiments, the ratiocan be about 1/3. Thus, in certain embodiments, the diameter can bebased on such ranges of ratios based on the foregoing example ranges ofdielectric layer thicknesses.

In certain implementations, the pitch 363 or the spacing between theedge of one well to the edge of a neighboring well can be selected basedon factors such as a desired density of wells and/or the diameter ofeach well. In certain embodiments, the pitch 363 can be in a range ofabout 1-10 mm or about 2-5 mm.

In certain embodiments, a ratio between the pitch 363 and the diameter364 can be about 1 to 5 or about 1.1 to 3. For example, in oneembodiment, the diameter 364 can be about 0.8 mm; thus, the pitch 613can be about 2 mm.

In certain implementations, a detection array can include from about50-10,000 wells 355. The number of wells can be greater or lesser thansuch an example range.

An upper readout electrode strip 360 is provided to each row of wellsand held at ground potential. A lower readout electrode strip 361 thatextends perpendicular to the upper strip 360 is also provided. The upperand lower readout strips 360, 361 provide a 2-dimensional readoutcapability for the wells 355.

In certain implementations, readout electrode strips can be configuredin a number of ways. FIG. 9A shows an example configuration 500 that canbe similar to the configuration associated with FIG. 7, where a firstset of readout electrode strips 504 extend in a first direction, and asecond set of strips 506 in a second direction (e.g., perpendicular tothe first direction). Each of the strips 504, 506 can include a numberof apertures for accommodating the openings 502 of the wells.

In certain situations, the readout configuration of FIG. 9A can resultin ambiguities in hit locations when more than one ion arrives on thearray close enough in time (e.g., substantially simultaneously). Toaddress such issues, certain embodiments of a readout configuration 510(FIG. 9B) can include three or more sets of readout electrode strips. Inthe example configuration 510, a first set is shown to have strips 514that extend along a first direction. Second and third sets of strips516, 518 are depicted as extending along two different directions (e.g,about 135 degrees and 45 degrees relative to the first direction) otherthan the first direction and a perpendicular of the first direction.Such angled configurations are sometimes referred to as “U” and “V”orientations (in the context of “X” and “Y” orientations of FIG. 9A) canfacilitate resolving of the foregoing ambiguities. Such resolvingtechniques and parameters such as angle selections can be achieved inknown manners.

Positive ions, produced in a low pressure (e.g., about 1-10 Torr)working gas above the detector plane, drift to the detector plane undera relatively weak (e.g., about 10-100V/cm) electric field provided byanode (relative to the electrode 354, and not shown) connected to apositive power supply. Focusing of the ions into the detector openings362, their acceleration and following charge multiplication process inthe well gas can be controlled by applying a negative voltage to thelower electrode (cathode 356) which provides a very highreduced-electric field across the well. To prevent damaging dischargesand sparks, this electrode can be made of highly resistive material(e.g., glass) and each detector cell can operate under a voltage wellbelow the field emission breakdown threshold.

For the example 3.2 mm-thick dielectric layer 352 shown in FIG. 8, andwhen the gas used is propane, air or water vapor at about 2 Torrpressure, the voltage applied to the cathode 356 can be in a range ofabout 650-850V. The resulting reduced-electric field (E/p) in the wellis about 2000V/(cm Torr) which is well above charge multiplicationthresholds for electrons and ions (about 30 and 70 V/(cm Torr),respectively, in propane).

A restricted avalanche in the well hole can start by positive ion impactionization and can develop due to ionizing collisions of secondaryelectrons and positive ions, with the former being responsible for mostof the charge multiplication. Ionization cross sections for positive ionimpact at low energy (e.g., 10-1000 eV) are scarce; however, availabledata for light ions (H, He) indicate that ionization cross section forpositive ions is about factor 2-10 smaller then for electrons of thesame energy. According to an estimate based on observation of ioninduced charge multiplication in low pressure gas, a probability for atleast one gas ionization on 0.1 mm ion path in 1 Torr propane under anelectric field of the order of 1000V/cm is below 10%.

Therefore a micro-pattern detector thickness on the order of about 0.1mm is likely too thin in some embodiments for high efficiency of singlepositive ion registration. In certain embodiments, a much thicker (e.g.,a few mm) detector structure can provide a high probability of ionimpact ionization as an ion passes through the cell.

It is also noted that attempts to increase the ion impact ionizationprobability by providing higher electric fields can result in fieldemission breakdowns that can permanently damage detector structures.

After the ion induced ionization occurs, the secondary electron(s)accelerating in the high electric field across the cell can initiate anavalanche propagating to the top of the cell. In such a high electricfield, the process, once started, goes on until substantially all of thegas in the cell is ionized. A discharge can develop, unless the electricfield is restricted by space charge effects or by an external device orcircuit (e.g., a resistor in the HV bias chain). In certain embodiments,the discharge stops when the voltage across the cell drops due to thehigh volume-resistivity of the cathode 357. This effect is similar tothe limited streamer process occurring in, for example, resistive platechambers (RPC).

The discharge can be restricted not only in time but in space, since itis substantially confined to the cell where it started. Propagation ofthe discharge due to UV photon feedback can be limited by the cellwalls; and the detector's reverse polarity prevents photoelectronemissions from the anode 354.

The avalanche electrons are cramped to the cell because the detector'selectric field configuration can change during the discharge developmentwithin a hole. It can be a dynamic process that can be characterized onthe basis of the electron trajectories described in reference to FIG. 7before and close to the end of the electron part of discharge. The firedcell field can change (e.g., drop) because the vast majority ofsecondary electrons produced at the top of the cell (avalanche head) canbe promptly collected on the readout strips, and the non-compensatedpositive charge of the avalanche ions can be screening the negativepotential of the cathode at the bottom of the cell. The field ofnon-fired neighboring cells can expand to the vacant region, trappingremaining electrons within the fired cell, and deflecting anysubsequently arriving ion into a nearby vacant cell. The remainingelectrons in the fired cell can be collected on the strips in the weakfield configuration or recombine with the ions slowly moving down tocathode positive charge cloud.

A recovery time of the fired cell can depend on the charge collectiontime and recharging time, and is estimated to be in the sub-μs to the μsrange. This fired cell recovery time should not affect the ion detectionefficiency because ions will likely arrive sufficiently spaced in time,due to their relative low drift velocities (e.g., about 1 mm/microsecondin 2 Torr propane, at 100 V/(cm Torr)). Further, as mentioned above,ions arriving during cell discharge are likely deflected to the neighborcells.

In certain embodiments, a signal from the readout strip can bedetermined by the charge accumulated in the cell's capacitor. Such acharge can be estimated as Q_(cell)=C_(cell) V, where C is thecapacitance and V is the operating voltage. Cell capacitance in theexample detector 351 is on the order of a few tens fF (femtofarad).Thus, for V of about 700V, charge (Q_(cell)) values in the tens pC rangecan be expected.

FIG. 8 shows a detector 150 that includes the various features describedin reference to FIG. 8. The example detector 150 can be manufacturedusing multilayer printed circuit board (PCB) technology. The exampledetector 150 includes an array 152 of holes 154 that form detectioncells (355 in FIG. 8). As previously mentioned, the example detector 150has a thickness of about 3.2 mm. Further, the array 152 has an activedetection area of approximately 2 cm×5 cm. There are 576 holes (154) inthe array 152.

To verify the signal amplitude representative of the charge (Q_(cell))output from a cell, the detector 150 of FIG. 8 was used. Moreparticularly, the detector PCB was mounted on a Teflon base withembedded glass cathode, so the HV electrode surface was exposed toworking gas only through detector holes. The detector assembly was theninstalled into a drift chamber enclosure providing controllable gasenvironment of about 0.1-10 Torr pressure and a drift field of up to1000V/cm. The chamber was also equipped with a collimated Am-241 alphasource and a Si detector defining alpha particle beam of about 2 mm indiameter and generally parallel to the detector plane and about 5 mmabove it. With this set-up (schematically depicted in FIG. 10A), signalsfrom the top electrode were acquired as negative pulses having about 200ns duration with amplitude of about 10 mV on a 50-Ohm load. Such asignal is representative of electron charge of about 20 pC, which isgenerally consistent with the tens pC range expected. The observedsignal amplitude corresponds to avalanche charge on the order of about10⁸ electrons, which is well above the Raether limit for breakdown ingases. That is, each cell can operate as an independent Geiger microcounter.

Measuring average ion arrival time at different anode voltages (hencedifferent ion drift field and velocity), it was verified that theregistered ions came from the alpha particle track. The ion drift timedistributions measured at anode voltages of 100V and 10V are shown inFIG. 10B. Also measured was the total background rate of the detectorresulting from sporadic discharges and ions from cosmic and backgroundradiation. For these measurements a working gas volume (about 2.5×5×5cm³ filled with propane at 2 Torr) was used. The background rate did notexceed 1 Hz for all of the 576 cells. These results show that the2-dimensional detector of FIG. 8 can be utilized as a planar iondetector in an ion time projection chamber (TPC).

FIGS. 11A and 11B show other examples of characterizing signalamplitudes representative of the charge (Q_(cell)) output from a cell ofthe detector 150 (FIG. 8). The data 220 shown in FIG. 11A were obtainedwith the detector operating at about 800V and in propane held at about 3Torr. The data 220 is fitted with a Polya distribution 222 that iscommonly used to characterize single-charge initiated avalancheprocesses.

As shown in FIG. 11A, the fit distribution 222 yields a mean chargeamplitude of about 35 pC, which is also generally consistent with thetens pC range expected. Such a consistency between the estimated range(tens pC) and data continues at other operating voltages as shown inFIG. 11B. A number of mean charge amplitude values are plotted asagainst operating voltages. As shown, the measured charge amplitudes arein a range of about 25 pC to 35 pC for voltages in a range of about 600Vto 800V. Further, the output charge amplitude increases linearly as afunction of voltage, also as expected.

In certain implementations of the present disclosure, radiation-inducedionization patterns in condensed matter and in equivalent gas models andof transport and multiplication processes within the different detectorscan be simulated. Monte Carlo radiation-transport codes can be appliedfor improving or optimizing the detector design and for evaluating itsperformance. Monte Carlo track structure codes can be improved tosimulate the transport of ions and secondary electrons in gaseous andcondensed media. The validity of interaction cross sections that areused in Monte Carlo codes can be tested using data from the detectors.

In certain implementations, the example ion induced impact ionizationdetector described in reference to FIGS. 7 and 8 or a similar detectordevice can be utilized to obtain experimental track-structure dataassociated with different radiation fields. Such experimental data canbe obtained at a number of facilities, including but not limited to,Loma Linda University's proton synchrotron (where protons up to 250 MeVcan be provided), Crocker Nuclear Laboratory at UC Davis (where protonsand light ions of low and intermediate energies can be provided from its76 inch isosynchronous cyclotron), and Brookhaven NationalLaboratory—NASA Space Radiation Laboratory (where protons and heavy ionsup to several GeV can be provided from the AGS Booster).

In addition to the foregoing examples of charged particle beams, datacan be obtained with radioactive sources including alpha, beta(electron) and gamma sources, representing a wide range of linear energytransfer (LET) values. Nanodosimetry data from a low-intensityradioactive neutron sources can also measured. Thus, a nanodosimetrictrack-structure database for validations and practical applications canbe developed and/or maintained.

Track-structure data measured with the example ion induced impactionization detector described in reference to FIGS. 7 and 8 has beenshown to be useful for estimating radiation effects observed in DNA andproducing meaningful quality factors for radiation protection.Measurements were made for frequency distributions of ionization eventsizes within a nanometric sensitive volume with rough dimensions of aDNA segment (about 4 nm diameter, FWHM and about 20 or 47 base pairslong) under various geometrical beam conditions. As described herein,FIGS. 2A and 2B show examples of nanodosimetric event size distributionsmeasured for various primary ions and energies, and a comparison ofexperimental and Monte-Carlo simulated distributions for protons. Thereis a good agreement between the measurements and simulations, down tofrequencies of about 2×10⁻³ (which corresponds to about 6 ions percluster). For larger clusters, there appears to be an excess of measuredions with respect to the simulation results.

While it is not desired or intended to be bound by any particulartheory, some experimental results suggest that these additional ionsseen in the foregoing experimental distribution may be caused by a raregas multiplication process which takes place in the intermediate vacuumof the ion acceleration channel below the detection cell aperture.

Additional studies correlating nanodosimetric data of various radiationfields with radiochemical and radiobiological data can validate variousmethodologies and translate such validated methodologies into practicalapplications. Utilizing one or more of the foregoing radiation fields,data for a number of more specific applications can be obtained; andsuch applications can include radiochemical yields of clusters ofhydrogen peroxide or other stable radiolysis products in nanoparticles;DNA double strand break and other complex damage yields in DNA modelsystems; DNA double strand break and other complex damage yields incells; CNS effects in suitable animal models; Cancer induction insuitable animal models. Additionally, existing in vitro and in vivo datacan be used to test nanodosimetric prediction models.

In certain implementations, one or more of the features described hereinallows imaging of a track passing through a volume of gas, which in turncan be scaled into tissue-equivalent (TE) scales and units. For suchsystems, resolution of positive ion imaging can be estimated.

Constraints imposed by ion diffusion on a track imaging detector can berepresented in tissue-equivalent (TE) units defined by the scalingfactor kp, where p is the pressure and k is a gas-dependent “dE/dx”scaling factor of an order of about 10⁻⁶-10⁻⁷. On the TE scale, the rmsbroadening due to a drift distance l_(TE) can be represented as:

${\Delta \; x_{TE}} = {\sqrt{k}\sqrt{2l_{TE}}\sqrt{\frac{D/K}{E/p}}}$

where D, K, and E represent the ion diffusion, ion mobility and electricfield, respectively.

Based on average D/K values, the rms TE resolution, Δx_(TE), can beestimated as a function of E/p. Such an estimate is depicted in FIG. 12for different gases. For a reasonable E/p value (e.g., approximately 100V/(cm Torr) used in at least some of the configurations describedherein), one can expect a typical TE resolution of ≦1.4 nm (rms) when anupper limit of TE drift distance is about 40 nm. Methane or water vaporcan yield even a better resolution, provided that a sufficiently highreduced-field can be maintained in these gases.

In a laboratory frame, gas pressure can define or influence actualdimensions and resolution of a detector, including the upper limit ofdrift length, l_(LAB), and the resolution Δx_(LAB), which in turn canprovide design parameters (e.g., pitch and/or cell size) related topixelization of a detector's array of cells.

For example, at a pressure of about 1 Torr propane, the resolution limitdue to ion diffusion is estimated to be about 0.5 mm (rms) for a driftof about 15 mm, thus a cell size of about 0.2 mm² can be adequate. Insome situations, increasing the pressure will not improve the resolutionon the TE scale, but will reduce it in the laboratory frame if the pixelsize remains unchanged. Consequently, a detector with smallerpixelization will be needed in such a case to provide the same TEresolution. Also, in some situations, the dimensions of the detector andthe drift length can scale with pressure, affecting the overall detectordesign.

In certain implementations, the gas choice and the reduced-electricfield can define the ion diffusion and the resolution Δx_(TE), on the TEscale for a given upper limit of TE drift length l_(TE), which in turncan be defined by the type of radiation to be imaged (e.g., l_(TE) ofabout 16 and 40 nm for 1 and 100 MeV protons, respectively). A typicalvalue of the rms TE resolution for ions drifting over the upper limit ofTE drift length of about 40 nm in propane can be about 1.4 nm or better.

In certain implementations, the present disclosure relates to systemsand methods for characterizing radiation in a manner that approximatesinteractions between radiation and nano-scale condensed matter. A DNAmolecule is an example of such a nano-scale condensed matter. There area number of other materials and situations where one or more techniquesof the present disclosure can be applied.

FIG. 13 schematically depicts a radiation measurement configuration 250where ionizing radiation (arrow 256) passes through a gaseousinteraction region 252. For the purpose of description, the interactionregion 252 can include one or more types of gases generally maintainedat a selected pressure or within a range of pressure so as to provide aninteraction cross-section σ₂ representative of a probability of ionizinginteraction between the ionizing radiation 256 and the gas molecules orparticles. Also, the interaction region 252 is depicted as having adimension of D2 generally along the direction of the ionizing radiation256.

In certain embodiments, and as described herein by way of examples,configuration of the gas and the interaction region dimension D2 can beselected so as to approximate interaction of the ionizing radiation 256with a much smaller and denser material such as a nano-scale condensedmatter 254 (depicted as having an interaction dimension of D1). Incertain embodiments, dimension and/or density scaling between thenano-scale interaction and the measured interaction can be achieved bymaking equivalent the interaction probabilities during passages throughthe nano-scale condensed matter 254 (dependent on cross-section σ₁) andthe gaseous region 252.

As described herein, such scaling can allow representative measurementsand characterization of nano-scale materials in more manageable and/orconvenient detection formats. For example, in situations where detectorelements having milli-meter range dimensions are utilized to approximateand characterize interactions in nano-meter range dimensions, there canbe an effective detection volume scaling expansion by a factor of about1 million.

FIG. 14 shows that in certain implementations, a process 260 can beimplemented to achieve such a scaled expansion of detection volume. In aprocess block 262, gas environment and interaction volume can beselected to approximate interaction of ionizing radiation with anano-scale condensed matter. In a process block 264, a detector can beprovided and configured to detect ionization products (e.g., positiveions) resulting from the interaction.

FIG. 15 schematically depicts an example of characterization of asmaller-scale matter (e.g., a nano-scale condensed matter) to alarger-scale detection volume. As shown, the example nano-scalecondensed matter can be a DNA strand 340, through which radiation 256passes. Such an interaction of radiation 256 with the DNA strand 340 isshown to be characterized by characterizing the interaction of the sameor similar radiation with a gas detector volume. Detection of ionizationproducts such as positive ions and characterization of the radiationtrack through the gas detector volume can provide a gas modelrepresentation of how radiation 256 interacts with the DNA molecule.Because the gas model can be based on more practical detectionparameters (e.g., mm range dimensions, gas choice, gas pressure, modesof detecting ionization products, etc.), modeling and characterizationof radiation's interaction with a nano-scale sized object such as a DNAstrand can be achieved in a more controlled and practical manner.

In certain embodiments, one or more features described herein can beimplemented in a detector capable of detecting spatial information forincident radiation (e.g., charged particles). FIG. 16 schematicallydepicts how a gaseous interaction volume 278, representative of thevolume 252 in FIG. 13, can be configured so as to allow detection ofionization products (e.g., positive ions 290). In certain embodiments,an interaction apparatus 270 can include first and second electrodes 272and 274 arranged to allow passage of ionizing radiation 256 through thegaseous volume 278 defined between the electrodes 272 and 274. Theelectrodes 272 and 274 are shown to be held at a potential difference ofΔV₁.

The interaction apparatus 270 is further shown to include a detectorlayer 280 disposed between the second electrode 274 and a thirdelectrode 276. The detector layer 280 and the associated electrodes 274,276 can be configured in manners similar to those described herein(e.g., FIGS. 7 and 8).

The second electrode 274 can act as a ground, and the first electrode272 can be held at a selected positive voltage +ΔV₁ relative to theground. Thus, for the gaseous volume 278, the first electrode 272 canact as an anode, and the second electrode 274 as a cathode.

The third electrode 276 can be held a selected negative voltage (−ΔV₂)relative to the ground. Thus, for the detector layer 280, the secondelectrode 274 can act as an anode, and the third electrode 276 as acathode.

The potential difference ΔV₁ for the gaseous volume 278 can be selectedso as to provide a relatively weak electric field (e.g., about 10 to 100V/cm) for a given gas type and pressure. Such a relatively weak electricfield can facilitate drifting (depicted as arrows 292) of positive ions290 generated from ionizing interactions and/or secondary interactions,without promoting charge multiplication processes within the volume 278.

The potential difference ΔV₂ for the detector layer 280 can be selectedto promote such charge multiplication processes. Various designconsiderations associated with such potential difference (such as gastype, gas pressure, spacing between electrodes) are described herein ingreater detail.

In certain situations, it may be desirable to be able to detect singleionization events. In each of such events, a positive ion and anelectron are generated from ionization. As described herein, suchpositive ions from ionized gas molecules can be detected with single-ionresolution, so as to allow characterization of radiation interactioneffects such as formation of large ionization clusters that contributeto damages to materials such as DNA strands.

FIG. 17 shows a process 300 that can be implemented to facilitate suchsingle ionization event characterization. In block 302, an interactionvolume can be configured as described herein. In block 304, a detector(e.g., detector layer 280 and associated electrodes in FIG. 16) asdescribed herein can be configured to allow detection of single ionsgenerated in the interaction volume.

FIG. 18 schematically depicts a portion of a detector 310 that can beconfigured to provide such a single-ion detection capability. Further,the detector 310 can have an array of detection elements to allowspatial characterization of the ionizing interactions occurring in theinteraction volume.

As shown, the detector 310 can include a plurality of wells 320 definedbetween two electrodes 274 and 276. In certain embodiments, theelectrodes 274 and 276 can be the second and third electrodes,respectively, described herein in reference to FIG. 16. Additionaldetails about the electrodes 274 and 276 (including an example of arrayreadout scheme via the ground electrode 274) and electric fieldsgenerated by the electrodes are described herein in greater detail.

In certain embodiments, the wells 320 can be formed on an insulatinglayer 314 such as a dielectric layer. The example wells 320 in FIG. 18are depicted as having a depth “d,” a width “w,” and an inter-wellspacing “s.” Selections of such dimensions are described herein ingreater detail. In certain embodiments, the wells 320 can be open on theside facing the interaction volume 278 such that gas pressure in thewells 320 can be generally same as that of the interaction volume 278.Such a feature can simplify the design and operation of the detector280.

In the example configuration shown in FIG. 18, a single ion 290 from aninteraction (not shown) in the volume 278 is depicted as drifting(dotted line 330) into the well 320 b. Due to the electric field E₂provided by the electrodes 274 and 276, and/or the gas configuration,the entering ion 290 can accelerate towards the cathode 276 and resultin multiplication of charges (e.g., avalanche 334) substantially in thewell 320 b. Details about such electric field and gas configurations, aswell as charge multiplication processes and detection thereof, aredescribed herein in greater detail.

As also described herein in greater detail (e.g., in reference to FIGS.6A and 6B), electric field formed at or about a given well opening canchange dynamically as ion-induced charge multiplication occurs in thewell (e.g., in 320 b). Such a dynamic nature of the electric field canpromote substantial containment of generated charges in the well, andalso promote deflection of additional incident ion(s) to otherunoccupied well(s). For example, the charge multiplication process inwell 170 b can result in an electric field change that promotesdeflection of another incident ion (depicted as dashed line 332) intoanother unoccupied well (e.g., a nearby well 320 a).

In certain implementations, an ion detector such as the example detector310 of FIG. 18 can be configured to be a part of system. Such a systemcan be configured to detect ions (primary and/or secondary) so as toallow characterization of interactions and/or processes that generatesuch ions. By way of an example, FIG. 19 shows a process 370 that can beconfigured to characterize interactions of ionizing radiation with avolume of low pressure gas by detecting ion products.

As described herein, such characterization of the interactions in lowpressure gas can be utilized for track-structure study of a number ofradiation-matter interaction settings. Such a study is sometimesreferred to as ionization pattern imaging, and can be applied tocharacterization of ionizing radiation with nano-scale condensed matterobjects such as DNA strands.

Referring to FIG. 19, the process 370 shows ionizing radiation (arrow372) entering a low pressure gas volume 374 and interacting with the gastherein. Interaction products such as primary and/or secondary ions(arrow 376) can be detected by an ion detector 378. In certainembodiments, such interaction products can be subjected to electricaland/or magnetic field to move (e.g., drift or accelerate) the ions tothe detector. The detection of the ions can yield analog signals (arrow380) from the detector 378, and such signals can be converted to digitalsignals 384 by an analog-to-digital converter (ADC) 382. Such digitizedsignals can be provided to a computing device 386 for further processingand/or analysis.

In certain embodiments, a system 390 having a number of components canbe configured to facilitate the example process 370 of FIG. 19. Thesystem 390 can include a power source 392 for providing power to, forexample, electrodes that define drift electric field in the interactiongas volume and ion detecting electric field in each of a number ofdetection cells. The system 390 can further include one or more housingcomponents 394, including, for example, a housing configured to providethe interaction gas volume. The system 390 can further include a dataacquisition (DAQ) component 396 configured to provide, for example,readout of signals from an array of detection cells and conversion ofsuch signals into representative digital signals for further processingby a computing device. The system 390 can have a detector component 398configured to provide one or more detector features and/or capabilitiesas described herein.

In certain implementations, the foregoing detector component 398 can bebased on one or more ion detector elements that are configured to allowefficient detection of single ions. FIG. 21 schematically depicts such adetector element 400.

In certain embodiments, a number of such detector elements 400 can bearranged in an array to allow spatial determination of ions' incidencelocations on the array. FIG. 22 schematically depicts such an array 410of detector elements 400.

In certain embodiments, such an array of ion detector elements can beused in an analytic system having an ion detection component. FIG. 23schematically depicts such a system 420 having an ion detector array410.

There are a number of analytic systems where the ion detector array 410can be implemented. FIGS. 24A-24C show some non-limiting examples of theanalytic system of FIG. 23. For example, FIG. 24A shows a dosimetersystem 430 having the ion detector array 410. Various configurations andoperating parameters are described herein in the context of such adosimeter system. However, similar detector elements and arrays thereofcan also be implemented in other analytic systems.

In certain embodiments, FIG. 24B shows that a mass spectrometer 440 or asimilar system can include the ion detector array 410 for detectingions. For example, ions that undergo mass separation due to electricand/or magnetic field(s) can be detected by the detector array 410 andspatial separation of the detected ions can be analyzed for massidentification.

In certain embodiments, FIG. 24C shows that a gas chromatograph 450 or asimilar system can include the ion detector array 410 for detectingions. For example, ions that emerge from a column exit can be detectedby the detector array 410 for analysis.

As used herein, mass spectrometry can include an analytical techniquefor determining the elemental composition or structure of a sample ormolecule. Mass spectrometers can include an instrument used to implementanalytical techniques of mass spectrometry. As used herein, gaschromatography can include an analytical technique for separatingcompounds in a mixture, wherein the mixture is vaporized but notdecomposed. A gas chromatograph can include an instrument used toimplement analytical techniques of gas chromatography.

The ion detector element and/or an array formed by such elements can beutilized in other systems. For example, ion detection configurations asdescribed herein can be implemented in systems for detecting very lowconcentrations of chemicals. An ion mobility spectrometer is an examplewhere trace concentrations of chemicals such as explosives, drugs, andchemical weapons can be detected. Such spectrometers can include one ormore features of the ion detectors as described herein to allowefficient and accurate characterization of ions.

In some embodiments, the ion induced impact ionization detector can becapable of providing new valuable data in the field of detector physics,related to ion interactions with gases and solids, light emission,multiplication processes in gas and advanced radiological imagingtechniques.

Some embodiments as described herein can be directed to ahigh-resolution, high-sensitivity 3D imaging track structure imagingdevices operating with low-density gases. The ion induced impactionization detectors as described herein can facilitate characterizationof the interaction of ionizing radiation with matter in the condensedphase. In one aspect, an approach to such a characterization can bebased on experimental techniques, such as nanodosimetry, and Monte Carlo(MC) track structure simulations. One can then, for example, relate thegas phase track structure and condensed phase track structure. Such anapproach can facilitate finding of track structure characteristics onthe micro- and nanometer-scale that are common to both phases and arerelevant for the effects of ionizing radiation on living cells and DNAnanostructures. In some implementations, experimental track structuredata may be used to benchmark MC codes.

As used herein, condensed matter can include cells, tissues, polymers,nanoelectronics and nucleic acid molecules such as DNA, in which anaberration may be induced. As used herein, aberration can include localdamage to condensed matter associated with ionization clusters that havebeen identified. As used herein, ionization clusters can include aplurality of ionization products, such as about 2-20 ions per cluster.In some cases ionization clusters can have about 6 ions per cluster.

An example application for radiation medicine and protection can relateto performing high-resolution track-structure studies to obtain animproved mechanistic understanding of radiation damage to DNA andchromosomes. For this, ionization tracks can be recorded in dilute gaswith a precision of about one tissue equivalent nm to study clusteringof ionizations on the DNA scale and over a track segment length of onetissue-equivalent Study of these clustering effects for different typesof radiation used in radiotherapy (high energy electrons, photons, andlight ions) and their comparison with the prediction of Monte Carlosimulations can be used to develop sophisticated mechanistic models ofradiation effect on DNA and other important biomolecules.

In some embodiments, a track structure-imaging system can be configuredto be capable of highly efficient and precise localization of ionizationpatterns on these scales. In some embodiments, ionization-inducedpositive ions can be recorded and deposited in low-pressure gas.

In certain implementations, modeling tissue with a low-pressure gastarget can allow expanding tissue scales, according to the “dE/dx ratio”scaling factor up to, for example, about 10⁶ for 1 Torr. Such a scalingfactor can be chosen according to the dimensions accessible by availablegaseous detectors, and/or the scale of the condensed matter beingstudied. In some embodiments, a ion induced impact ionization detectorconfigured to provide substantially full track structure and singlecharge sensitivity can provide a resolution of sub-nm tissue-equivalentprecision over a micrometer tissue-equivalent range. The same dimensionscan also be relevant to non-biological applications such as thoserelating to nanoelectronics devices.

As used herein, “nanometer equivalent resolution” can include resolutionof sub-nm tissue-equivalent precision over a micrometertissue-equivalent range and similar dimensions in nanoelectronicsdevices. Nanometer equivalent resolution may relate to a spatialseparation of individual energy-deposition events (e.g., electron-ion,electron-hole pairs) in condensed matter. In some embodiments, thespatial separation can be of the same order of magnitude as the lateraldimensions of a DNA molecule or strand and of some elements innanoelectronics, i.e., in the nanometer domain. For example, nanometerequivalent resolution includes a precision of about one tissueequivalent nm, where such precision can be useful for study ofclustering of ionizations on the DNA scale and over a track segmentlength of one tissue-equivalent μm.

In certain implementations, the ion detector element 400 of FIG. 21 canbe configured to include one or more of the features described herein.In certain embodiments, such features can include those described inreference to FIGS. 7-9.

In certain implementations, such an ion detector element 400 can beoperated in a limited Geiger mode (e.g., fired/not fired). In certainimplementations of such an operating mode, one or more featuresassociated with the ion detector element 400 can be configured toprovide a gas environment that under super-stress by the electric fieldapplied to the well of the detector element 400. Such a state can beanalogous to a super-cooled or super-heated state of liquid, where thephase transition (freezing or boiling) has not occurred even after thetemperature has gone below the freezing temperature or above the boilingtemperature. In such a state, a slight disturbance and/or a seedcondition can trigger a rapid phase transition.

In certain implementations, the super-stressed gas environment of theion detector element 400 can be achieved by providing an electric fieldto the well so that the electric field strength is higher than athreshold value or range of values associated with breakdown of gas.Such a threshold value or range can depend on factors such as type ofgas, pressure and/or temperature. In certain implementations, theelectric field strength can be selected to be also higher than athreshold value or range of values associated with ion multiplication.Such a threshold value or range is typically higher than thecorresponding gas breakdown threshold value or range.

In certain implementations, the electric field strength can be selectedbased on one or more of the foregoing threshold values, and to be lowerthan a threshold value or range of values associated with field emissionbreakdown at a surface of the well. Such a value or range can depend onthe material associated with the well surface.

Voltages associated with the foregoing electric field strengths candepend on factors such as separation distance of the electrodes andelectrode geometries. Thus, an applied voltage can be selected for agiven well size (e.g., depth), gas type, gas pressure and/or gastemperature so as to yield a desired electric field strength having oneor more of the foregoing properties.

For example, the example detector configuration of FIG. 8 can besupplied with a voltage of about 600 to 900 V between the electrodes toyield a desired gas condition when the detection configuration includespropane, air or water vapor at about 2 Torr in a well having a depth ofabout 3.2 mm.

In certain detection situations, sensitivity of a detector and itsstability can be balanced. For example, a detector configured to behighly sensitive can be triggered easily by a particle (e.g., anelectron) other than a desired particle (e.g., an ion). In the contextof the super-tensioned gas environment, an electron can easily triggerthe limited Geiger process. In certain implementations of the presentdisclosure, however, likelihood of such electrons entering the well ofan ion detector element (e.g., 400 in FIG. 21) can be reduced by areversed polarity of the voltage biasing configuration.

For example, and referring to FIGS. 10A, 16 and 18, certain embodimentsof the present disclosure can be configured so that the deep end of awell can be held at a negative potential relative the well's opening.Further, an anode that facilitates drifting of positive ions towards thedetector can be held at a positive potential relative to the well'sopening. Accordingly, electrons in the vicinity of the well will besubjected to a force that directs electrons away from the well (towardsthe anode).

In certain embodiments, an ion detection cell having one or more of thefeatures described herein can operate with a relatively large dead timetypically associated with the Geiger operation mode. Despite such aproperty, a high detection efficiency for single ions can be provided byuse of a large number of such cells distributed and configured to reducethe likelihood of two or more ions entering a single detection cell.

Further, due to the diffusion of ions generated in a low-pressure gasvolume, even ions originating from the same deposition point are likelyto be registered in different cells. Hence, the effective efficiency canbe relatively high.

As used herein, a gas can include multi-atomic gases and gas mixtures tosimulate biological and semiconductor media. For example, a gas caninclude one or more of the following gasses: propane, ambient air, andwater vapor. In certain implementations, the gas can be ionized byinitiating an avalanche breakdown of gas in a well, whereby the ionizinginduces charges that are multiplied thereby forming a detectable signal.

As used herein, low pressure or low pressure gas can include a gas at apressure that is less than about 100 Torr. In certain implementations,low pressure can include a pressure in a range of about 1 to 10 Torr.

As used herein, a breakdown potential can include a point at whichnon-conducting gas becomes conductive as governed by the pd product(p=pressure, d=inter-electrode gap distance) and the Townsend mechanism.In some embodiments, the breakdown potential can occur when an electricfield exceeds a particular value, wherein an electron avalanche starts,for example, due to multiplication of some primary electrons in cascadeionization. In some embodiments, the breakdown potential can be about0.1-1.5 cm Torr at an operating pressure of about 1-10 Torr, and aninter-electrode gap, distance of between 2-5 mm. In some embodiments,the breakdown potential can be at a pd value of about 0.6 cm Torr (about2 Torr and about 3.2 mm gap), for example for propane, air and watervapor, can be about 400-600V assuming a substantially uniform electricfield. In some embodiments, the field emission breakdown potential canbe above about 5 kV for a detector, wherein no breakdown was observed atpd<0.00003 cm Torr (better than 0.0001 Torr vacuum and 5 kV over 3.2 mmgap).

As used herein, E/p value (electric field strength divided by pressure)as used herein is sometimes referred to as “reduced-electric field.”Thus, for example ranges of E and p of about 10-100 V/cm and about 1-10Torr, respectively, the corresponding reduced-electric field (E/p) canhave a value in a range of about 1-100 V/(cm Torr).

The terms “approximately,” “about,” and “substantially” as used hereinrepresent an amount close to the stated amount that still performs thedesired function or achieves the desired result. For example, the terms“approximately”, “about”, and “substantially” may refer to an amountthat is within less than 10% of, within less than 5% of, within lessthan 1% of, within less than 0.1% of, and within less than 0.01% of thestated amount. The term “at least a portion of” as used hereinrepresents an amount of a whole that comprises an amount of the wholethat may include the whole. For example, the term “a portion of” mayrefer to an amount that is greater than 0.01% of, greater than 0.1% of,greater than 1% of, greater than 10% of, greater than 20% of, greaterthan 30% of, greater than 40% of, greater than 50% of, greater than 60%,greater than 70% of, greater than 80% of, greater than 90% of, greaterthan 95% of, greater than 99% of, and 100% of the whole.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The word “coupled”, as generally usedherein, refers to two or more elements that may be either directlyconnected, or connected by way of one or more intermediate elements.Additionally, the words “herein,” “above,” “below,” and words of similarimport, when used in this application, shall refer to this applicationas a whole and not to any particular portions of this application. Wherethe context permits, words in the above Detailed Description using thesingular or plural number may also include the plural or singular numberrespectively. The word “or” in reference to a list of two or more items,that word covers all of the following interpretations of the word: anyof the items in the list, all of the items in the list, and anycombination of the items in the list.

The above detailed description of embodiments of the invention is notintended to be exhaustive or to limit the invention to the precise formdisclosed above. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example, whileprocesses or blocks are presented in a given order, alternativeembodiments may perform routines having steps, or employ systems havingblocks, in a different order, and some processes or blocks may bedeleted, moved, added, subdivided, combined, and/or modified. Each ofthese processes or blocks may be implemented in a variety of differentways. Also, while processes or blocks are at times shown as beingperformed in series, these processes or blocks may instead be performedin parallel, or may be performed at different times.

The teachings of the invention provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the disclosure. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the disclosure. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the disclosure.

1. An ion induced impact ionization detector comprising: an anode havinga first side and a second side, and defining a plurality of apertures; adielectric layer having a first side and second side, wherein the firstside of the dielectric layer is positioned adjacent the first side ofanode, and wherein the dielectric layer has a thickness of approximately1-50 mm; a plurality of wells extending through the dielectric layer,the plurality of apertures of the anode positioned relative to theplurality of wells so as to define openings between the plurality ofwells and the second side of the anode; a cathode positioned adjacentthe second side of the dielectric layer forming a bottom of each of theplurality of wells.
 2. The ion induced impact ionization detector ofclaim 1, wherein the thickness is in a range of approximately 1 to 5 mm.3. The ion induced impact ionization detector of claim 1, wherein thethickness is in a range of approximately 2 to 5 mm.
 4. The ion inducedimpact ionization detector of claim 1, wherein the anode comprises oneor more layers of conductive material.
 5. The ion induced impactionization detector of claim 1, wherein the cathode comprises aresistive cathode layer.
 6. The ion induced impact ionization detectorof claim 1, wherein the anode and the cathode are separated by adistance that is substantially the same as the thickness of thedielectric layer.
 7. The ion induced impact ionization detector of claim1, wherein the ion induced impact ionization detector is sensitive to asingle ionization event in each of the plurality of wells.
 8. The ioninduced impact ionization detector of claim 1, further comprising afirst plurality of readout strips configured in a first orientation anddisposed on the first side of the dielectric layer; and a secondplurality of readout strips configured in a second orientation anddisposed on the first plurality of readout strips so as to allowidentification of a well that has detected an ion.
 9. The ion inducedimpact ionization detector of claim 8, wherein the first and secondorientations are substantially perpendicular so as to define X and Yorientations.
 10. The ion induced impact ionization detector of claim 8,further comprising a third plurality of readout strips configured in athird orientation and disposed on the second plurality of readout stripsso as to allow determination of more than one wells that detected ionssubstantially simultaneously.
 11. The ion induced impact ionizationdetector of claim 10, wherein the first, second and third orientationsdefine X, U and V orientations.
 12. The ion induced impact ionizationdetector of claim 1, wherein each of the plurality of wells has acylindrical shape, and each of the openings defines a circle having adiameter.
 13. The ion induced impact ionization detector of claim 12,wherein the diameter is selected to be in a range of about one-tenth ofthe thickness to one thickness.
 14. The ion induced impact ionizationdetector of claim 12, wherein the diameter is selected to be in a rangeof about one-tenth of the thickness to one thickness.
 15. The ioninduced impact ionization detector of claim 14, wherein the diameter isselected to be in a range of about one-fourth of the thickness toone-third of the thickness.
 16. The ion induced impact ionizationdetector of claim 12, wherein the plurality of wells are arranged in anarray so as to define a pitch distance between the edges of twoneighboring openings, the pitch selected so that a ratio between thepitch and the diameter is in a range of about 1 to
 5. 17. The ioninduced impact ionization detector of claim 16, wherein the ratiobetween the pitch and the diameter is in a range of about 1.1 to
 3. 18.A detector system comprising: an enclosure having a volume of lowpressure gas; a drift anode disposed within the volume of low pressuregas; the ion induced impact ionization detector of claim 1 disposedwithin the volume of low pressure gas so as to define a detection gasvolume between the drift anode and the anode of the ion induced impactionization detector, the wells having substantially the same lowpressure as in the volume of low pressure gas due to the openings; andan electrical power supply coupled to the drift anode, and the anode andcathode of the ion induced impact ionization detector, such that theanode of the ion induced impact ionization detector is at a groundpotential, the drift anode is at a positive potential relative to theground, and the cathode is at a negative potential relative to theground, the positive potential selected to provide a first electricfield in the detection gas volume for drifting of a positive ion towardsthe anode of the ion induced impact ionization detector, the negativepotential selected to provide a limited Geiger avalanche in the wellwhere the positive ion drifts into.
 19. The detector system of claim 18,wherein the low pressure of the gas is in a range of about 1 to 100Torr.
 20. The detector system of claim 19, wherein the low pressure ofthe gas is in a range of about 1 to 10 Torr.
 21. The detector system ofclaim 18, wherein the negative potential is selected such that anelectric field strength within the well is greater than a thresholdvalue associated with breakdown of the gas in the well.
 22. The detectorsystem of claim 21, wherein the negative potential is selected such thatthe electric field strength within the well is less than a thresholdvalue associated with field emission breakdown at a surface of the well.23. The detector system of claim 18, wherein the negative potential isselected such that an electric field strength within the well puts thegas within the well in a super-tensioned state.
 24. The detector systemof claim 18, wherein one or more dimensions of the well, spacing betweenthe wells, and the negative potential is selected such that an electricfield formed within the well is capable of changing as the ion inducedavalanche progresses to direct another incoming ion to another nearbywell.
 25. A method of detecting particles comprising: detecting one ormore positive ions using the ion induced impact ionization detector ofclaim
 1. 26. The method of claim 25 further comprising subjecting thesecond side of the anode to a gas; maintaining the environmentsurrounding the ion induced impact ionization detector at a pressure ofless than about 10 Torr.
 27. The method of claim 26 further comprisingapplying a negative voltage to the cathode; maintaining the anode atground potential such that an avalanche breakdown of the gas in thewells results when a positive ion enters the sell, the avalancheresulting in a detectable collection of charges.
 28. The method of claim27 wherein: the negative voltage applied is in a range of about600-900V; the operating pressure is selected to be less than about 10Torr.
 29. The method of claim 28 wherein: the operating pressure isselected to be less than about 2 Torr; and the negative voltage isselected so as to yield a quantity of electric field strength divided bypressure (E/p) has a value of about 2000V/(cm Torr).
 30. A method formodeling a sample of condensed matter, the method comprising:identifying ionization clusters responsible for local damage to saidcondensed matter.
 31. The method of claim 30, wherein the condensedmatter is selected from the group consisting of cells, polymers,nanoelectronics and nucleic acid molecules.
 32. The method of claim 30further comprising subjecting the condensed matter to ionizing radiationproduced by the ion induced impact ionization detector of claim 1,wherein said subjecting step induces an aberration in said condensedmatter.
 33. The method of claim 32 further comprising assessing effectsof said ionizing radiation on said condensed matter.
 34. The method ofclaim 33, wherein said effects are selected from a DNA double strandbreak, a central nervous system effect, and cancer induction.
 35. Amethod of track ion detection, the method comprising: imaging a spatialdistribution of initial energy deposits in condensed matter by detectingpositive ions using the ion induced impact ionization detector ofclaim
 1. 36. The method of claim 35 further comprising correlatingmeasurements from said imaging step with radiation effects in saidcondensed matter.
 37. The method of claim 35, wherein the ion inducedimpact ionization detector provides a substantially full topology of theionization pattern of track segments and resolves single and clusteredionization events along the radiation track over a length in condensedmatter.
 38. A track ion detector comprising the ion induced impactionization detector of claim
 1. 39. A mass spectrometer, a ion mobilityspectrometer or a gas chromatograph comprising the ion induced impactionization detector of claim
 1. 40. An ion detector element comprising:an anode; an insulator layer having a first side and a second side, thefirst side of the insulator layer disposed adjacent the anode, theinsulator layer having a thickness in a range of approximately 1-5 mm; acathode disposed adjacent the second side of the insulator layer;wherein the insulator layer defines a well that extends between thefirst and second sides of the insulator layer, the well provided with agas at a pressure of approximately 1-10 Torr, the anode and cathodeprovided with an electrical potential difference of approximately600-900 V.